The Pulse

The shady truth about shade

If you've ever been sunburnt after spending time under a covered grandstand or beach umbrella, you'll know all shade is not equal. How do you spot the safest shade?

[Image source: stock.xchng | dynamix]

When it comes to choosing shade to protect you from UV, there's more to it than meets the eye.

Just ask anyone who's come home from a day at the cricket mystified that they're sunburnt, despite spending the entire time in a covered section of the grandstand.

Or perhaps you've noticed your skin turn pink, even though you resisted temptation and stayed wholly in the shade of your beach umbrella when you went to the beach.

It turns out not all shade is equal, and even if you spend long hours out of direct sunlight, you can still receive quite a lot of UV. This is because ultraviolet radiation reaches your skin in two ways:

directly, as radiation from the sun,

indirectly, as radiation that's been reflected from the atmosphere above, and/or bounced back from surfaces such as sand, concrete or even grass.

When you're sitting under an umbrella or covered grandstand, a large amount of the UV you receive is indirect, says Terry Slevin, education and research director with Cancer Council WA.

If there's nothing else around to block the sun, the shielding effect of the umbrella or grandstand blocks only the direct UV.

"Shade is great. It's far better than not having any," Slevin says. "But it's not perfect. If you're exclusively relying on shade, you can be a bit surprised and disappointed at the end of the day. You might find yourself with a bit of pink skin  or worse."

Umbrellas and sun

A single umbrella in an open space provides limited sun protection, Slevin says.

Even if the umbrella is made of fabric that blocks 100 per cent of UV, and you manage to stay completely out of direct sunlight, the UV dose is cut by only about half. This is because the umbrella blocks only the direct UV (plus a very small amount of the indirect UV). This means it is about as effective as a sunscreen with an SPF of 2.

But if the umbrella is used on a beach, where it is surrounded by water and highly reflective sand, the protection offered may be even lower still because of the UV reflected underneath the umbrella canopy from the surface of the sand.

"I'm not saying don't get a beach umbrella. It's certainly better than nothing at all," says Slevin. "But by itself, it probably isn't going to do the job you want done."

If it is possible to place your beach umbrella near a wall or building, that would further cut some of the indirect UV, Slevin says.

Or better still, consider a beach 'tent' or igloo rather than a brolly as the side walls of the tent provide more protection. (Then all you've got to worry about is getting it back in its storage pouch without making a spectacle of yourself on the sand  especially challenging when there's a bit of wind around.)

Spotting the safest shade

You can get an idea of the amount of indirect UV you're being exposed to by the amount of open sky you can see from the shaded area.

So if you are standing in the shadow of a wall, receiving no direct sun, and you can see only about half the hemisphere of the sky (because the rest is obscured by the wall), then you are protected from about half the indirect UV.

An urban environment with tall buildings can significantly reduce the view of the sky and therefore the exposure to indirect UV, Slevin says.

And larger shaded areas provide more protection than small ones (you'll also be better protected if you're not right at the edge of the shade, however large it is).

The cricket experience

So yes, if you're noticing you're a bit pink after a day in the shade at the cricket, it might be more than a post-match glow of excitement.

Depending on your position in the grandstand, it's quite possible indirect UV is to blame, Slevin says  especially if you were in the shade "but you could see a big chunk of the sky beyond the extent of the shade". UV reflected from surfaces like short grass or concrete may also play a role.

His advice? "Take your eyes off the pitch and look up. If you can see lots of sky, chances are there's going to be at least some level of diffuse [scattered from the atmosphere] and reflected UV getting through to you."

As with the beach brolly story, the take home message is that shade alone doesn't always cut it.

And in those instances, skimpy swimmers or a muscle-flashing singlet don't cover a lot of skin. So you still need to remember to use protective measures like sunscreen and other clothing.